Objectives: 1. The HPr component of the Mycoplasma PTS has been extensively purified but remains contaminated by at least four other proteins. 2. In vitro complementation of the PTS components of Mycoplasma, Spiroplasma, Escherichia coli and Arthrobacter pyridinolis show that Mycoplasma and Spiroplasma exhibit complete and reciprocal complementation whereas Mycoplasma shows nonreciprocal complementation with E. coli and A. pyridinolis. 3. Spiroplasma citri, the recently discovered mycoplasma-like organism exhibits a PTS which complements completely with that of Mycoplasma thus confirming its kinship with the organisms of the genus Mycoplasma.